1. Field of the Invention
The present invention relates to a solid-state imaging device. More particularly, the present invention relates to a solid-state imaging device in which a plurality of pixels are arranged in a matrix and to a camera utilizing the same.
2. Description of the Background Art
In a solid-state imaging device such as CCD and MOS image sensors, it is required to increase the light-condensing rate in order to improve image quality. To increase the light-condensing rate, a converging lens is used in general. With reference to the accompanying figures, a common structure of a solid-state imaging device will be described below.
FIG. 9 is a schematic top plan view for illustrating the positional relationship between pixels and light-sensitive areas in a solid-state imaging device in which a plurality of pixels are arranged in a matrix.
The solid-state imaging device illustrated in FIG. 9 includes a semiconductor substrate 1, pixels 2, and light-sensitive areas 3. As a semiconductor substrate 1, a p-type silicon substrate is generally used. On the semiconductor substrate 1, a plurality of pixels 2 are arranged in a matrix. Note that the pixels 2 shown herein are the pixels as projected onto a principal surface of the semiconductor substrate 1. Points m which are the centers of the pixels 2 as projected onto the semiconductor substrate 1 (hereinafter, each such point is referred to as “a center of the pixel) are arranged at regular intervals in both longitudinal and horizontal directions. Each pixel 2 includes a photoelectric conversion portion (not shown) which converts incident light into a signal charge. In a predetermined area of the pixel 2 is formed a light-sensitive area 3 for enabling the photoelectric conversion portion to receive incident light. A light-sensitive area 3 of the same shape is formed in each pixel 2, with the center of the light-sensitive area 3 coinciding with the center m of the pixel 2. Therefore, the centers p of light-sensitive areas 3 are also arranged at regular intervals in both longitudinal and horizontal directions.
Next, with reference to FIG. 10 and FIG. 11, the structures of the pixels 2 and the light-sensitive areas 3 are described more specifically. FIG. 10 is a top view of a solid-state imaging device. FIG. 11 shows a cross-sectional structure, taken along line A-B, of the solid-state imaging device shown in FIG. 10. The solid-state imaging device shown in FIG. 10 and FIG. 11 includes a semiconductor substrate 1, pixels 2, light-sensitive areas 3, photoelectric conversion portions 4, drain areas 5, gate electrodes 6, device separation areas 7, scanning circuit portions 8, a light-shielding film 22, a color filter 9, and converging lenses 10.
Each pixel 2 includes apart of a semiconductor substrate 1, a photoelectric conversion portion 4 (including a photodiode), a drain area 5, a gate electrode 6, a scanning circuit portion 8, and a device separation area 7. The photoelectric conversion portion 4, the drain area 5, and the device separation area 7 are formed on the semiconductor substrate 1. Between the photoelectric conversion portion 4 and the drain area 5 on the semiconductor substrate 1 is formed the gate electrode 6. On the surface of the semiconductor substrate 1, on which the gate electrode 6 is formed, an insulating film 21 is provided. On the insulating film 21 is formed the light-shielding film 22, which leaves a predetermined area within the photoelectric conversion portion 4 uncovered so as to define the light-sensitive area 3. On the light-shielding film 22 is formed the color filter 9, upon which a converging lens 10 is further disposed. The converging lens 10 is provided corresponding to each pixel 2. Thus, a solid-state imaging device in which one pixel is constructed as one cell (unit) is realized.
Each converging lens 10, which is provided corresponding to one pixel 2, is arranged so that an area occupied by its corresponding pixel 2 within a principal surface of the semiconductor substrate 1 can be utilized as efficiently as possible, in order to allow as much light to be converged on the pixel 2 as possible. That is, the converging lens 10 is arranged so that the center of the converging lens 10 coincides with the center m of the pixel 2 when seen from directly above the principal surface of the substrate. Similarly, the light-sensitive area 3, which is formed on each pixel 2, is arranged so that the center m of the pixel 2 and the center p of the light-sensitive area 3 coincide with each other when seen from directly above the principal surface of the substrate, in order to increase the light-condensing rate. If the solid-state imaging device is structured in this manner, incident light 11 on the pixel 2 is focused by the converging lens 10 and then travels toward the center m of the pixel 2. As a result, the incident light is converged on the center p of the light-sensitive area 3, so that a high light-condensing rate can be achieved.
In recent years, with the miniaturization of solid-state imaging devices, there is a desire to miniaturize pixels. To satisfy such a demand, as is described in Japanese Laid-Open Patent Publication No. 8-316448, for example, a proposal has been made in which neighboring pixels are allowed to share a gate electrode or a drain area so that miniaturization of the pixels can be achieved. The details thereof are described below, with respect to an exemplary solid-state imaging device in which every two pixels are constructed as one cell (unit).
FIG. 12 is a top view of a solid-state imaging device which is structured such that every two pixels constitute a unit 2a of pixels (a cell). The solid-state imaging device shown in FIG. 12 is identical to the solid-state imaging device shown in FIG. 10, except that every two neighboring pixels 2 share a drain area 5a. In this manner, miniaturization of pixels can be achieved by removing the device separation area 7, which is situated between the drain area 5 and the photoelectric conversion portion 4 in FIG. 10, and allowing the two pixels 2 to share the drain area 5a. 
However, although miniaturization of pixels 2 is realized, the solid-state imaging device shown in FIG. 12 has a problem in that the light-condensing rate with respect to the entire solid-state imaging device becomes lower. As a result, aberration, color shading, sensitivity shading, the deterioration of image sensitivity, and the like occur.
A detailed description is made below, with reference to the accompanying figures.
FIG. 13 is a schematic top plan view for illustrating positional relationships between pixels 2 and light-sensitive areas 3 on the semiconductor substrate 1. Since two pixels 2 share a drain area 5a within a unit 2a of pixels as described above, the center m of the pixel 2 and the center p of the light-sensitive area 3 within each pixel 2 are offset from each other when seen from directly above a principal surface of the substrate. Therefore, although on the substrate the centers m of the pixels 2 are positioned at regular intervals, the centers p of the light-sensitive areas 3 are not positioned at regular intervals as are the centers m of the pixels 2, but are arranged such that the intervals are unevenly spaced.
FIG. 14 shows a cross-sectional structure, taken along line A-B, of the solid-state imaging device as shown in FIG. 12. As was described with reference to FIG. 13, the center m of a pixel 2 and the center p of its light-sensitive area 3 are offset from each other when seen from directly above a principal surface of the substrate. Although incident light 11 on the pixel 2 is focused by a converging lens 10 and then travels toward the center m of the pixel 2 as described above, the incident light 11 is not converged onto the center p of the light-sensitive area 3. As a result, the light-receiving sensitivity of the light-sensitive area 3 is reduced as compared with the case of the solid-state imaging device illustrated in FIG. 11. It would be conceivable to arrange each converging lens 10 so that its center is adjusted to the center p of the light-sensitive area 3 in order to increase the light-condensing rate. In this case, however, because as described above the centers p of the light-sensitive areas 3 on the substrate are not arranged at regular intervals, the configuration of converging lenses 10 would inevitably become complicated. Moreover, if the position of each converging lens 10 were to be adjusted to the center p of the light-sensitive area 3, the size of the converging lens 10 would have to become small. Hence, the entire area of the pixel 2 would not be covered by the smaller converging lens 10. Therefore, the entire area of the pixel 2 could not be utilized efficiently. As a result, the light-condensing rate would be reduced.